code: func (b *Builtin) Call(operands ...*Term) *Term {
  	call := make(Call, len(operands)+1)
  	call[0] = NewTerm(b.Ref())
  	for i := range operands {
  		call[i+1] = operands[i]
  	}
  	return NewTerm(call)
  }
docs: // Call creates a new term for the built-in with the given operands.