Yes. And you said > A program that emits "Yes" on every input will decide some property of programs with zero false negatives. Followed by > any semantic pr

Yes. And you said > A program that emits "Yes" on every input will decide some property of programs with zero false negatives. Followed by > any semantic property that is not either always true or always false for all program executions So what you said is your decider always outputs true. That's not an interesting property, because it's true for all inputs. Btw what is the point of your argument? It still doesn't refute my initial statement. If you want to determine an interesting property of program like leaks, or automatic lifetime calculation or whether output is square of input, you run into Rice Theorem, which makes the problem undecidable. In other words it's impossible to get correct yes and no algorithmically.