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11 votes
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Ascending chain condition for 1-element normal closures in a free group

Let $F$ be a free group of finite rank. Does $F$ satisfy the ascending chain condition on normal subgroups each of which is a normal closure of one element? In other words, can there exist elements $ …
Ashot Minasyan's user avatar
7 votes
Accepted

Products of subgroups of a free group

The answer is negative even if $A$ is finitely generated. Here is a simple construction. Let $F$ be the free group on $\{x,y,z\}$ and let $A=\langle x,y \rangle$. Then there is a natural retraction $ …
Ashot Minasyan's user avatar
7 votes
3 answers
514 views

Membership to double cosets in free groups

Is there an elementary and efficient algorithm for testing the membership to a double coset of f.g. subgroups in a free group? Has this membership problem been implemented in GAP/Magma? More precise …
Ashot Minasyan's user avatar
4 votes
Accepted

Measuring products of finitely generated subgroups of free groups

The answer is yes. Let's prove this by induction on $n$. If $n=1$, then by M. Hall's theorem there is a finite index subgroup $K \leqslant F$ such that $H_1 \subseteq K$ and $|F:K|>1/\epsilon$. Choo …
Ashot Minasyan's user avatar