If fx=x-1-x, where [x] is the greatest integer less than or equal to x, then
f1+0=-1, f1-0=0
f1+0=0 = f1-0
limx→1 f(x) exists
limx→1 f(x) does exists
f1+0= limh→0 1+h-1-1+h=limh→0 x-1=-1f1-0= limh→0 1-h-1-1-h= limh→0 h-0=0