setxkbmap gb -model pc105 -option caps:ctrl_modifier,altwin:swap_alt_win,lv3:ralt_switch_multikey

KeyPress event, serial 37, synthetic NO, window 0x3c00001,
    root 0x9e, subw 0x0, time 5963911, (-671,413), root:(1601,498),
    state 0x0, keycode 133 (keysym 0xffe9, Alt_L), same_screen YES,
    XLookupString gives 0 bytes:
    XmbLookupString gives 0 bytes:
    XFilterEvent returns: False

KeyRelease event, serial 37, synthetic NO, window 0x3c00001,
    root 0x9e, subw 0x0, time 5964047, (-671,413), root:(1601,498),
    state 0x8, keycode 133 (keysym 0xffe9, Alt_L), same_screen YES,
    XLookupString gives 0 bytes:
    XFilterEvent returns: False