# What's the difference between Acfg and ALLcfg

In computational theory, and talking about CFGs, Turing Machines, and so forth I haven't a satisfactory explanation or definition for what ATM means versus ALLTM or the same or similar uses with CFGs, etc. Does the single A stand for any, some, one, or all instances of the class whether it's a TM, a CFG, or anything else? Conversely, ETM and EQTM are obvious as to what they mean.

• Those notations may not be fixed completely. Please edit the question to add a reference to the textbook you are using. – John L. Jun 9 '19 at 22:32
• $ALL_{TM}$ usually means the set of turing machines which accept any input (that is, $L(M) = \Sigma^*$). – rici Jun 10 '19 at 2:26