 Windsurfing is a major attraction on Ibiza and Formentera; equipment can be hired at escuelas de windsurfing as well as many resorts.
People cannot hire windsurfing gear at Formentera and Ibiza. 
mnli hypothesis: People cannot hire windsurfing gear at Formentera and Ibiza.  premise:  Windsurfing is a major attraction on Ibiza and Formentera; equipment can be hired at escuelas de windsurfing as well as many resorts.