1 alias id "nat" = "cic:/Coq/Init/Datatypes/nat.ind#xpointer(1/1)".
2 alias num (instance 0) = "natural number".
3 alias symbol "eq" (instance 0) = "leibnitz's equality".
4 alias symbol "plus" (instance 0) = "natural plus".
7 a = b \to b + a = a + a.
9 rewrite right H in (? ? % ?).