Table:
text: 1986 Mexican Grand Prix
Classification
Classification
Driver Constructor_ Laps Time_Retired Grid
Gerhard Berger Benetton - BMW 68 1:33:18.700 4
Alain Prost McLaren - TAG 68 + 25.438 6
Ayrton Senna Lotus - Renault 68 + 52.513 1
Nelson Piquet Williams - Honda 67 + 1 Lap 2
Nigel Mansell Williams - Honda 67 + 1 Lap 3
Philippe Alliot Ligier - Renault 67 + 1 Lap 10
Thierry Boutsen Arrows - BMW 66 + 2 Laps 21
Andrea de Cesaris Minardi - Motori Moderni 66 + 2 Laps 22
Christian Danner Arrows - BMW 66 + 2 Laps 20
Jonathan Palmer Zakspeed 65 Out of Fuel 18

Question: Who is the constructor when the laps are less than 68, the grid is more than 20 and the driver is Thierry Boutsen for the 1986 Mexican Grand Prix?