Map2[f, exp] is equivalent to Map if Nterms[exp] > 0, otherwise Map2[f, exp] gives f[exp].
Map2[f, exp]
Map
Nterms[exp] > 0
f[exp]
Overview, NTerms.
Map2[f, a - b]
f(a)+f(−b)f(a)+f(-b)f(a)+f(−b)
Map2[f, x]
f(x)f(x)f(x)
Map2[f, {a, b, c}]
f({a,b,c})f(\{a,b,c\})f({a,b,c})
Map2[f, 1]
f(1)f(1)f(1)