I saw someone on the internet wonder if Ed and Al are capable of doing flame alchemy because they have seen Truth. This bothered me, since this would negate the idea that flame alchemy was difficult to learn and that via destroying Hawkeye's tattoo, it would be possible to avert the existence of another flame alchemist (vol. 14).
Someone suggested that it's possible from an omake where Ed finds Roy's lost gloves, puts them on, and creates an explosion. (Click to see images.)
However, this is an omake so I doubt it can be taken completely seriously, and moreover, Ed does not seem to have any of the technique Roy has honed. Yet at least with flame alchemy, where manipulation of gas concentrations is necessary (vol. 1), technique and precision seem to be crucial. Given this, I would normally expect to be what Ed describes as a "rebound".
Does seeing truth indeed allow alchemists to circumvent the normal learning process, provided that they at least have a rough idea of what materials are involved and the arrays needed, if they are lacking in the specific techniques that would normally be indicated by the ability to use an array? (The latter bit is necessary; otherwise, there's no reason why Ed and Al don't learn for three years how the philosopher's stone is created.)
Of the four alchemists who have seen Truth in FMA, all of them seem to only have gained the ability to perform alchemy without an array, and if I'm not mistaken, we only ever see them perform transmutations that they can be presumed to have already known beforehand. We do see Ed use Scar's deconstruction technique once, but unlike with flame alchemy, there's no question of needing the correct combination of materials or precise "technique" here.
I am looking for answers based on the manga.