Can we get something equivalent to $\mathsf{ZFC2}$ by naively allowing the separation and replacement to range over second-order wffs?
5584
How strong is this second-order version of ZFC?
5187
An analogue of Hensel's lifting for Fibonacci numbers
71945
How to reduce circuit elements of a decomposed $C^2(U)$ operation?
1712
$ d_1,d_2\mid n\iff {\rm lcm}(d_1,d_2)\mid n\ $ [LCM Universal Property]
60731
Factorization of a map between CW complexes
46211
$(K[x,y,z]/(x^2+y^3+z^7))_{(x,y,z)}$ is a UFD.
9118
Polynomial division: an obvious trick? [reducing mod $\textit{simpler}$ multiples]
135282
How can I construct a sequence of injections $\langle f_\alpha\colon\alpha\to\omega\mid\alpha<\omega_1\rangle$ with a particular coherence property?
22842
The Interpretation of $|\psi|^2$ and the No-Clone Theorem
100816
Mandelbrot-like sets for functions other than $f(z)=z^2+c$?
3217
Construction of uncountably many non-isomorphic linear (total) orderings of natural numbers
53432
What is the algebraic closure of $\mathbb F_q$?
28368
Is there a constructible flat pairing function?
107772
Separability of functions with compact support
83713
If $z,w\in \mathbb{C}^{\times}$, then $|z+w|=|z|+|w|$ iff $w=tz$ for some $t\gt 0$
107839
Are there nontrivial equations for hyperoperations above exponentiation?
137982
Show that $\textbf{ZF}$ shows $\phi$ is $\Delta_1$