The term minus is represented by the sign - . It has two different meanings:

1) Negation (unary minus):

Example: Today the temperature is minus 5 degrees outside.

2) Subtraction (binary minus):

Example: Yesterday the temperature was minus 5 degrees, and it has decreased by 3 degrees since then. Hence, today the temperature is minus 8 degrees,
which we express in ordinary algebra as \; -5 \,- \,3 \, = \, -8 .

Note: In the last example, the first minus sign to the left of the = sign represents negation, and so does the minus sign to the right. In contrast, the second minus sign to the left of the = sign represents subtraction.

Using the appropriate form of equality, the temperature example would be more clearly expressed as

\; \stackrel {\mathrm{neg}}{-} 5 \, \stackrel {\mathrm{sub}}{-} \, 3 \, \equiv \; \stackrel {\mathrm{neg}}{-} 8 .