Geodesic
The semigroup of continuous selfmaps of I has infinitely many ideals
Glasgow mathematical journal, Tome 34 (1992) no. 1, pp. 27-33

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Let I denote the interval [0,1] in its usual topology and let S = S(I) be the semigroup of continuous mappings of I into itself with function composition as the semigroup operation. In a survey talk given at Oberwolfach in 1989 (see [5]), K. D. Magill Jr. pointed out that some elementary algebraic properties of S are still unknown. We shall answer one of the questions he raised (which appears as Problem 4.6 in [5] and which he had asked earlier, as long ago as 1975 [3]) by showing that S has infinitely many distinct two-sided ideals. In fact, we shall produce an infinite descending sequence of distinct ideals. As Magill points out, this also solves his Problem 4.5: S has infinitely many distinct congruences. We believe that S must have c distinct ideals, but we have been unable to prove this. 
Baker, J. W.; Pym, J. S. The semigroup of continuous selfmaps of I has infinitely many ideals. Glasgow mathematical journal, Tome 34 (1992) no. 1, pp. 27-33. doi: 10.1017/S001708950000851X
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