$(x\in y\land y\in x)\to\bot$ in FOL
88982
Prove that for any two sets $A$ and $B$, $A\notin B$ or $B\notin A$
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
17
First Order Language for vector spaces over fields
93707
Formal proof for $q \land \neg q \vdash r \land \neg r$
3092
Find where $r(t)=$ hits the $x-y$ plane
155136
$x\in \{\{\{x\}\}\}$ or not?
136427
Given $∃y.∀x.p(x,y)$, use the Fitch system to prove $∀x.∃y.p(x,y)$
138931
Show that $||x+y||\cdot||x-y||\le||x||^2+||y||^2$
15865
Show that $X = \{ (x,y) \in\mathbb{R}^2\mid x \in \mathbb{Q}\text{ or }y \in \mathbb{Q}\}$ is path connected.
154698
Union of Cartesian products: $X \times (Y \cup Z)= (X \times Y) \cup(X\times Z)$
155974
Show $||Tx||_2 \leq ||(v_n)||_2 \cdot ||x||_{\infty}$
140682
Proving a property of a Logic Formal Language
78463
Prove that $\sup \{-x \mid x \in A\} = -\inf\{x\mid x \in A\}$
56156
Composition and Onto Functions
56878
Proof that $a\mid b \land b\mid c \Rightarrow a\mid c $
151947
Finding a pair of functions with properties
74312
If Y is complete then B(X,Y) is complete