A, B, C, etc. refers to people.

1|2 refers to the two sides of the first condom. 3|4 refers to the two sides of the second condom. etc.

(a) two condoms

A, B = men; C, D = women.

1|2 3|4 A has sex with C. 1 4 1|2 A has sex with D. 1 4 2 3|4 1|2 B has sex with C. 1 3 4 2 3|4 B has sex with D. 1 3 4 2

(b) two condoms

A = man; B, C, D = women. A B C D

1|2 3|4 A has sex with B. 1 4 1|2 A has sex with C. 1 4 2 1|2 4|3 A has sex with D. 1 4 2 3

A, B, C = men; D = woman.

1|2 3|4 A has sex with D. 1 4 3|4 B has sex with D. 1 3 4 2|1 3|4 C has sex with D. 1 3 2 4

(c) two condoms

A, B, C = men.

1|2 3|4 A has sex with B. 1 4 4|3 2|1 B has sex with A. 1 4 3|4 C has sex with B. 1 4 3 4|3 B has sex with C. 1 4 3 1|2 4|3 A has sex with C. 1 4 3 3|4 2|1 C has sex with A. 1 4 3

(d) k+1 condoms

A = woman; B, C, D, ... = men

1|2 A has sex with B. 1 2 1|2 4|3 A has sex with C. 1 2 3 1|2 3|4 A has sex with D. 1 2 3 4 and so on, after the first man there is one condom used for every two men

(e) ceiling(m/2 + 2n/3) see Ilan Vardi, Computational Recreations in Mathematica, Addison Wesley, 1991, p. 205

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