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I have no router and the installer never prompted for an IP address.
Two wireless stations could be connected using Ad-Hoc mode (so called iBSS) or using Access Point (BSS mode).
If you do not have access point, you can try to configure Ad-Hoc:
WiFi is a complex subject (much more complex than Ethernet based on copper twisted-pair cable), there is a whole book dedicated to Wifi administration: