[1] Department of Applied Mathematics,
[2] Charles University,undefined
[3] Malostranské nám. 25,undefined
[4] 118 00 Praha 1,undefined
[5] Czech Republic matousek@kam.mff.cuni.cz,undefined
[6] Department of Mathematics,undefined
[7] Heriot—Watt University,undefined
[8] Edinburgh EH14 4AS,undefined
[9] Scotland petr@ma.hw.ac.uk ,undefined