In physics literature, a transformation such as formula_120 might be written without any further explanation. The formal mathematical interpretation of this is that the field formula_107 is an element of formula_122 where formula_123 Thus, properly speaking, the field should be written as formula_124 which behaves under charge conjugation as formula_125 It is very tempting, but not quite formally correct to just multiply these out, to move around the location of this minus sign; this mostly "just works", but a failure to track it properly will lead to confusion.