+1 : @$\mathbb{N}$@ @$\rightarrow$@ @$\mathbb{N}$@
+1 n = suc n -- not use lambda

@$\lambda$@+1 : @$\mathbb{N}$@ @$\rightarrow$@ @$\mathbb{N}$@
@$\lambda$@+1 = (\n @$\rightarrow$@ suc n)   -- use lambda