NAME
	sum_mappings - summarize two mappings into one

SYNTAX
	mapping sum_mappigs(mapping a,mapping b,function A,function AB,
		function B);

DESCRIPTION
	Returns a mapping built like this: for every index that is present
	in a but not b, set this index to the value of A(a[index]) and for
	all indexes that are present in b but not a B(b[index]) and all
	that are present in both are set to AB(a[index],b[index]) If given
	an integer instead of one of the functions, 0 is assumed.

SEE ALSO
	map_mapping, sum_arrays, map_array