Concave implies subadditive
7825
If $f$ is a concave function and $f(0) \geq 0$ then $f(a+b) \leq f(a) + f(b)$ for all $a,b >0$
35857
Characterization of log-convexity
64197
Subgradients of non-convex functions
72659
How can we define convexity in one dimension?
116382
Showing convexity of a function with the restriction over an arbitrary line
72468
Open and closed balls in $C[a,b]$
144250
subideals of an ideal
54764
Given a real function $g$ satisfying certain conditions, can we construct a convex $h$ with $h \le g$?
60887
$d_A(x) = \inf_{a \in A} \|x-a\|$ is convex if and only if $A$ is convex
57943
If $G$ is a convex set, prove that $\mathbb{C}\cup\{\infty\}\setminus G$ is connected.
15491
Prove that $f:\mathbb R^n\to\mathbb R$ is affine if and only if it is convex and concave
5738
Cancellation of addition on convex sets
51302
Show that the operator norm is submultiplicative
45380
Surjectivity implies injectivity and conversely
85819
A non-polyhedral pair $(X,A)$ with both $X$ and $A$ polyhedral
71829
Is closure of convex subset of $X$ is again a convex subset of $X$?
15924
Convexity and strong lower semicontinuity imply weak lower semicontinuity