$hash{0}{plus}{0} = 0;
$hash{0}{plus}{1} = 1;
$hash{1}{plus}{0} = 1;
$hash{1}{plus}{1} = 10;

%plus = %hash{}{plus}{};
#  (or something like it)
# should yield: 
# $plus{0}{0} = 0;
# $plus{0}{1} = 1;
# $plus{1}{0} = 1;
# $plus{1}{1} = 10;