There is only a single logical data type, the BOOLEAN. The BOOLEAN
type recognizes the following STRING values as "literals":
TRUE
YES
FALSE
NO
Table 1. Primitive logical types
Primitive
Size
Data type
BOOLEAN
1 byte
EGL evaluates a BOOLEAN type variable as either
TRUE or FALSE, and also recognizes the values YES (same as TRUE) and
NO (same as FALSE) as Boolean literals.