Are research prerequisites broken?

[Bobe]

I noticed a while into my career that I had been able to unlock certain research nodes even though only one of the prerequisites had been met. Is this how it's supposed to be? I thought all prerequisites would have to be unlocked in order to progress.

As far as I can tell the only thing that changes once all node prerequisites are met is that node becomes visible.

I'm not sure if the issue is mod related. I played completely stock for a while, but I'm not sure if I got far enough in the tech tree to experience prerequisites before putting mods on.

[Damien_The_Unbeliever]

With two exceptions, most nodes with pre-requisites treat them as "OR" prerequisites rather than "AND" - so long as you have one of the pre-requisites, you can unlock the node.

I'm not sure if that's the actual intention but it has existed in this form for quite a long time.

If you consult the wiki, you'll see the pre-requisites listed - only Ion Propulsion and Nuclear Propulsion require multiple pre-requisites.

[Bobe]

Assuming this is the intended format, they should either qualify the prerequisites by saying "At least one of the following:", or "All of the following:", or something to that effect.

Perhaps nodes could receive a small discount if you have unlocked all prior technology, so you could go straight for the higher tier, or progress everything slowly and save on science points in the long term.