Drew replied: > A60 is 1.d4 Nf6 2.c4 c5 3.d5 e6 [4.Nf3] which is a transposition of > 1.d4 Nf6 2.c4 e6 3.Nf3 c5 4.d5
But this is not really answering my question. If "1.d4 Nf6 2.c4 c5 3.d5 e6 4.Nf3" is A60, then logically "1.d4 Nf6 2.c4 c5 3.d5 e6 4.Nf3 b5" should also be A60, but it is E10. Note that a delayed b5 will also be assigned to A60, e.g. "1.d4 Nf6 2.c4 c5 3.d5 e6 4.Nf3 g6 4.g3 b5". With other words the (equal) lines 1.d4 Nf6 2.c4 e6 3.Nf3 c5 4.d5 b5 1.d4 Nf6 2.c4 c5 3.d5 e6 4.Nf3 b5 are an exception because they are belonging to E10, but any other line starting with either "1.d4 Nf6 2.c4 e6 3.Nf3 c5 4.d5" or "1.d4 Nf6 2.c4 c5 3.d5 e6 4.Nf3" , not immediately followed by b5, will be assigned to A60. Why this exception?
