"(C = A - B, but C + B != A)");
}
C = A.minus(B);
C.plusEquals(B);
try {
A.plusEquals(S);
errorCount = try_failure(errorCount,
"plusEquals conformance check... ",
"nonconformance not raised");
} catch (IllegalArgumentException e) {
try_success("plusEquals conformance check... ", "");