89                     months dm = ym1 - ym2;  in test_arithmetic()
90                     assert((dm < months{0}) == (ym1 < ym2));  in test_arithmetic()
91                     assert((dm == months{0}) == (ym1 == ym2));  in test_arithmetic()
92                     assert((dm > months{0}) == (ym1 > ym2));  in test_arithmetic()
122     assert(ym + months{0} == ym2);  in test_arithemtic_not_ok()
123     assert(ym - months{0} == ym2);  in test_arithemtic_not_ok()
124     assert(ym - ym2 == months{0});  in test_arithemtic_not_ok()
125     assert(ym2 - ym == months{0});  in test_arithemtic_not_ok()
128     ymc += months{0};  in test_arithemtic_not_ok()
135     assert(ym + months{4} == ym2);  in test_arithemtic_not_ok()
136     assert(ym2 - ym == months{4});  in test_arithemtic_not_ok()
137     assert(ym - ym2 == -months{4});  in test_arithemtic_not_ok()
140     ymc += months{4};  in test_arithemtic_not_ok()
147     assert(ym - months{4} == ym2);  in test_arithemtic_not_ok()
148     assert(ym2 - ym == -months{4});  in test_arithemtic_not_ok()
149     assert(ym - ym2 == months{4});  in test_arithemtic_not_ok()
152     ymc -= months{4};  in test_arithemtic_not_ok()
160     assert(ym + months{16} == ym2);  in test_arithemtic_not_ok()
161     assert(ym2 - ym == months{16});  in test_arithemtic_not_ok()
162     assert(ym - ym2 == -months{16});  in test_arithemtic_not_ok()
165     ymc += months{16};  in test_arithemtic_not_ok()
172     assert(ym - months{16} == ym2);  in test_arithemtic_not_ok()
173     assert(ym2 - ym == -months{16});  in test_arithemtic_not_ok()
174     assert(ym - ym2 == months(16));  in test_arithemtic_not_ok()
177     ymc -= months{16};  in test_arithemtic_not_ok()
184     assert(ym2 - ym == months{11});  in test_arithemtic_not_ok()
185     assert(ym - ym2 == -months{11});  in test_arithemtic_not_ok()
190     assert(ym2 - ym == months{23});  in test_arithemtic_not_ok()
191     assert(ym - ym2 == -months{23});  in test_arithemtic_not_ok()
218     static_assert(ym2 - ym1 == months{11}, "");  in main()
219     static_assert(ym1 - ym2 == -months{11}, "");  in main()