Many psionic abilities in the GURPS Psionic Powers book do not have a fixed cost per level.To deal with this, I used modifiers as a replacement for ability levels.You only need 1 level active at a time (i.e. you do not need Interruption_2 and Interruption_1 active, only Interruption_2).
The underscore is related to the irregular points per level of some psionic abilities.If a skill is red and says this is the problem, go to the related ability and activate a modifier to "level up" your ability.All levels 1+ fulfil this requirement.