The only other distinction between == and =:= is for integers and floats. Integers are not =:= to the corresponding float, but are ==, so it has nothing to do

The only other distinction between == and =:= is for integers and floats. Integers are not =:= to the corresponding float, but are ==, so it has nothing to do with closeness. -0.0 is a weird dumb non mathematical value that IEEE 754 put in (for example the standardized value for sqrt(-0.0) is not even justifiable based on their choices). I think they didn't want 1/(1/-Inf) to be Inf, or something. In the end think of erlang's "==" as "equal in value" and "=:=" as "equal in representation in memory". Now if you really want to raise the hackles of someone using Erlang, should ask why integers and floats don't have a well ordering, and what you should do when you sort them.