In a work of Just, Miller, Scheepers and Szeptycki it was asked whether certain diagonalization properties for sequences of open covers are provably closed under taking finite or countable unions. In a recent work, Scheepers proved that one of the properties in question is closed under taking countable unions. After surveying the known results, we show that none of the remaining classes is prov...

The concept of affordances, introduced by J.J. Gibson in Psychology, has recently attracted interest in autonomous robotics towards the development of cognitive systems. In earlier work (Şahin et al., Adaptive Behavior, vol.15(4), pp. 447-472, 2007), we reviewed the uses of this concept in different fields and proposed a formalism to use affordances at different levels of robot control. In this...