(q − r) diagram for the 13 interacting binaries that were used in our analysis. Algols (q < 1) are at the left of the vertical line q = 1.0. The ten direct impact systems are located above the curve ω_d (filled squares). The three systems with a transient accretion disk around the gainer are located between the curves ω_min and ω_d (filled circles). Permanent accretion disks would be located below ω_min. Systems with q > 1 have not reached Algol characteristics yet.