#x in [-1,0] rArr -1lexle0.............<<1>>#.
#-2y in [-2,2] rArr -2le-2yle2...................<<2>>#.
#:. <<1>>+<<2>> rArr -1-2lex-2yle0+2, ie., #
# -3lex-2yle2#.
#rArr (x-2y) in [-3,2]=[-3,0]uu[0,2]#.
#rArr (x-2y) in [-3,0], or, (x-2y) in [0,2]#.
#"If, "(x-2y) in [-3,0], -3le(x-2y)le0#
#rArr0le(x-2y)^2le9, or,#
#(x-2y)^2 in [0,9].............................<<3>>#.
#"Similarly, "(x-2y) in [0,2]rArr (x-2y)^2 in [0,4]...<<4>>#.
Combining #<<3,4>>#, we find,
#(x-2y)^2 in [0,9]uu[0,4]#.
#rArr (x-2y)^2 in [0,9]#.