"Source: Text/Commut/RngDiff.text";
"Line: 607";
"Date: Thu Sep 25 14:47:46 2025";
"Main: Fri Sep 26 14:29:19 2025";
// original file: Text/Commut/RngDiff.text, line: 607
// Example: H121E9 ()
print "Example: H121E9";
ei := GetEchoInput();
SetEchoInput(true);
F<z>:=RationalDifferentialField(Rationals());
S<t>:=DifferentialLaurentSeriesRing(Rationals());
HasProjectiveDerivation(F);
assert not $1;
HasProjectiveDerivation(ChangeDerivation(F,z));
assert $1;
HasZeroDerivation(F);
assert not $1;
HasProjectiveDerivation(S);
assert $1;
HasProjectiveDerivation(ChangeDerivation(S,S!3));
assert not $1;
HasZeroDerivation(S);
assert not $1;
SetEchoInput(ei);
