## 12. `perpendicular()`

: Return the opposite
orientation

In this application, we often use 0 to denote a horizontal
slot and 1 to denote a vertical slot.
This utility routine inverts the sense of such a value.
Assuming the value is either 0 or 1, subtracting the
value from 1 will give the opposite value.

kkck

# - - - p e r p e n d i c u l a r
def perpendicular ( isV ):
'''Invert an 'isV' flag.
[ if isV is 0 ->
return 1
if isV is 1 ->
return 0 ]
'''
return 1-isV