Prove that the set of palindromes are not regular languages
86858
Prove that the set of palindromes are not regular languages using the pumping lemma.
138669
proving that elements of a sequence are pairwise coprime
113342
Confusion of the decidability of $(N,s)$
37183
Show that the set of all $x$ such that $x \in P$ and $x \notin Q$ exists
118022
Show that a group of order $180$ is not simple.
49385
Proving $\forall x (A\to B) \to(A \to \forall x B):x\notin \mbox{free}(A)$ in a Hilbert system where it is not an axiom
140194
Using natural deduction to prove that $p \implies q \vdash \lnot p \lor q$
61602
Binary strings (words) proof
4383
Finitely generated monoids - how to show that there is not first order set axiomatizing them.
158728
Using induction for an easy proof for formal languages
93022
Prove that a given recursion sequence converges
90074
Show that the sequence $1,2,3,4,5,6,7,8,9,1,0,1,1,1,2,1,3,1,4,1,5,1,6,1,7,1,8,1,9,2,0,2,1,\cdots$ isn't periodic
93606
Showing that $C[0,1]$ is not complete
74361
Unit test cases for Python palindrome
128305
$PGL(n, F)=PSL(n, F)$
85799
Finding languages such that $L_{1} \subseteq L_{2} \subseteq L_{3}$ where $L_{1}, L_{3} \notin \mathbb{R}$, $L_{2} \in \mathbb{R}$
137646
show that language $L'$ is regular (given $L$ regular)