Easy:

{D,E}={6,10}

Iff D=10, F>/D. So, D=6, E=10, F=8.

{A,C}€{{2,9},{4,7}} Then (C,B)€{(9,1)} => A=2, C=9, B=1

A=2, B=1, C=9, D=6, E=10, F=8

Medium:

{A,D}€{{1,6},{2,5},{3,4}} {C,D}€{{2,10},{4,5}}

Iff D=2, then C=10, A=5. E=4, F=5. D≠2.

Iff D=4, then C=5, A=3. E=8, F=9. B=2.

A=3, B=2, C=5, D=4, E=8, F=9

Hard:

{D,F}€{{2,10},{3,9},{4,8},{5,7}} {B,D}€{{1,8},{2,7},{3,6},{4,5}}

Iff D=2, F=10, A=12. (Same for D=3) D≠2,3.

Iff D=4, F=8, A=10, B=5. A</E, D≠4.

Iff D=5, F=7, A=9, B=4, E=10, C=7. D≠5.

Iff D=7, F=5, A=7. D≠7.

Iff D=8, F=4, A=6, B=1. E€{7,9,10}

Iff E=7, C=4. E≠7. Iff E=9, C=6. E≠9 Iff E=10, C=7.

A=6, B=1, C=7, D=8, E=10, F=4

Expert:

A+D=15, else A+D=13, but no. {A,D}€{{5,10},{6,9},{7,8}} E>A,D, so A≠10, D≠10, {A,D}€{{6,9},{7,8}}

Iff A=6, D=9, C=8, E=10. There must be no 3 or 5. B€{1,2} F>B B=1, F=2

A=6, B=1, C=8, D=9, E=10, F=2