# is the name for the not equal function. I suggest
that you use a different name. A function can be declared
additive, but if it is a function of two or more
arguments, the function is additive in just its
first argument (as is sum and integrate).
(%i1) infix(@);
(%o1) @
(%i2) declare("@",additive);
(%o2) DONE
(%i3) (a+b) @ (c + d);
(%o3) @(b,d+c)+@(a,d+c)
(%i4) describe("additive");
......
To make @ multi-additive, you'll need to write
a definition for @; something like
"@"(a,b) := ....).
Barton