I would like to rename variables "a_tick6 a_Cf1 a_Cf21 a_Cf2"
into "tick6 Cf1 Cf21 Cf2" (Namely, I would like to remove "a_" from all the variables.)

However, I do not know how to create variable "without a_" by using for each command.

Can somebody help me?
Thank you very much.