RDF.XSD.Numeric.subtract

You're seeing just the function subtract, go back to RDF.XSD.Numeric module for more information.

Subtracts two numeric literals.

For xsd:float or xsd:double values, if one of the operands is a zero or a finite number and the other is INF or -INF, an infinity of the appropriate sign is returned. If both operands are INF or -INF, NaN is returned. If one of the operands is INF and the other is -INF, an infinity of the appropriate sign is returned.

If one of the given arguments is not a numeric literal or a value which can be coerced into a numeric literal, nil is returned.

see http://www.w3.org/TR/xpath-functions/#func-numeric-subtract