Supporters of Mir Hossein Mousavi have worn green ribbons in protest
After a week of unprecedented mass protests in Iran over the presidential election results, the BBC's John Simpson reflects on the parallels between the 1979 revolution and current events.
The last time I found myself in Valy Asr avenue in Tehran, shouldering my way through a shouting, sweating, half-excited, half-frightened crowd - in order to get television pictures of a fire that was sending up a column of choking black smoke into the sky - it was 1979 and I was 30 years younger.
Things have changed a bit now, of course.
Back then, people did not have mobile phones to hold up in the air and take snapshots or videos of what was going on and send them round the world.
There were not nearly so many young women among the demonstrators.
Then, people did not automatically spot who I worked for.
Now, vast numbers of people in Tehran watch BBC television news broadcasts in English and Persian, and it is hard to get through a crowd without being spotted.
Of course it is all different in one way. These people are not protesting against an absolute monarch who has been trying to force Western-style modernisation on to a mostly conservative population.
Instead, they are furious that their ultra-conservative government should - as they see it - have insulted their intelligence by fixing the result of the presidential election in such a crude way.
Tehran has seen mass demonstrations by all sides since the disputed election
Of course, even to suggest there might be any similarities at all with the revolution of 1979 enrages the government here.
But if you remember those days as well as I do, you can spot the parallels at once.
The demonstrators are very much the same mixture of educated, well-to-do north Tehraners and lower-middle class.
They are often more religious people who do not have a lot more in common with each other than a dislike of the way the government tells them how to live their lives, and a feeling that there is serious corruption and inefficiency at the top.
The big difference is that in 1979, the tough, heavily-bearded ultra-religious characters you used to see marching in the demonstrations are now on the other side.
They are known as the basijis, the shock troops of the Islamic Revolution.
They are the ones who shot down eight demonstrators, in a crowd which was attacking their barracks near Azadi Square a few days ago.
President Ahmadinejad swept to power in 2005
Yet although the comparison between the things that happened in the streets then and what is happening now is very striking to someone who has seen them both, there are deeper and more important parallels.
The Shah could never decide whether he was an autocrat or a liberal; increasingly isolated, he would swing backwards and forwards, first shooting down the protesters and imposing martial law, then offering concessions.
On Thursday, President Ahmadinejad - having earlier accused the demonstrators of acting like angry football fans - told the nation on television that he only meant the violent ones, and that his election victory belonged to everyone.
A lot of people here are speculating that the Supreme Leader of the Islamic Republic, the spiritual leader Ayatollah Khamenei, is leaving Ahmadinejad to twist in the wind, having realised that he has become so unpopular he could bring down the whole structure of Islamic power.
And then a contrary view says that it is really all about the moderate religious and political leaders trying to save the system by ditching Khamenei as well as Ahmadinejad.
Ayatollah Khamenei has strongly denied the election was rigged
When I go out into the streets now and see the crowds with their green ribbons and scarves and face-paint and balloons, it occurs to me that I am looking at a coalition of interests as complex as the one that marched along the same streets 30 years ago.
Then, liberal, middle-class, Westernised people joined in the marches eagerly because they thought the religious leaders under Ayatollah Khomeini would bring about a better Iran.
Now they are joining in because they think the marches in support of Mir Hossein Mousavi will bring down the Islamic Revolution.
Yet for his part Mr Mousavi hopes he can rescue the Islamic Revolution and make it better.
I remember interviewing him in the 1980s, and I cannot say he impressed me then as being particularly liberal; rather the contrary.
But he is certainly different now.
The Tiananmen uprising is a reminder that not all student revolts succeed
So who is going to win?
In late 1978 I would go from earnest discussions with the revolutionaries in the streets, and talk to British and American diplomats who would promise me that the Shah would get out of this one as he had got out of so much trouble in the past.
Ten weeks later he had gone and the revolutionaries had won.
But just because people seem brave and attractive and believe intensely in freedom, that is not enough to make sure they will get rid of the system they have come to hate.
It did not happen in Tiananmen Square, after all.
In other words, just because I watched a revolution happen here 30 years ago, it does not mean that very much the same sort of people marching through exactly the same streets will automatically win now.
Or if they do, it will take more than simply marching.
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